(JTA) — The United Kingdom has the largest number of synagogues in its history, but membership in those institutions is at its lowest in decades, according to a newly published report.

In its report titled “Synagogue membership in the United Kingdom in 2016,” the Institute for Jewish Policy Research counted 454 Jewish houses of worship with a combined membership of fewer than 80,000 households.

The report, which was published Tuesday, reveals that 79,597 Jewish households across the United Kingdom held synagogue membership in 2016, down from 99,763 in 1990 — a 20 percent decline over a quarter of a century.

According to the authors, the decline is only partially related to assimilation and can be explained primarily by demographic forces – a general decline in the number of Jewish households that exist in the United Kingdom.

In the United Kingdom, where approximately 250,000 Jews live, many synagogues employ a membership system in which worshippers who pray there regularly pay fees for activities and maintenance.

Orthodox synagogues had the largest membership at 53 percent, the report said, down from 66 percent in 1990. Reform and Liberal shares, at 19 and 8 percent in 2016, have slightly increased over that period.

“The affiliated British Jewish community is changing. The mainstream Orthodox center is in numerical decline, whilst stricter forms of Orthodoxy are in the ascendancy,” Jonathan Boyd, the executive director of the Institute for Jewish Policy Research, said in a statement about the report. “Because the more progressive wing is largely stable, representing just under a third of the total, the trends point to a future in which stricter forms of Orthodoxy will hold an increasingly prominent position, not only in synagogue membership, but in how Judaism is practiced and how Judaism is seen and understood by others.”

Three-quarters of the U.K. synagogues are in Greater London and the adjacent areas of South Hertfordshire and South-West Essex, and 11 percent are in Greater Manchester. Half of all synagogue members belong to synagogues that are situated in just five areas in the London area: Barnet, Westminster, Hertsmere, Redbridge and Stamford Hill.